Catalytic transvinylation of vinyl esters with carboxylic acids to form compounds useful in the manufacture of plastics, as polymeric coatings, adhesives or internal plasticizers is a well known reaction. Early accounts of this process used as a catalyst a mercury salt and a strong acid such as disclosed in U.S. Pat. No. 2,299,862 (1942) and U.S. Pat. No. 2,997,494 (1961). Mercuric sulfate is described as the catalyst for such a reaction in U.S. Pat. No. 3,000,918 (1961) and U.S. Pat. No. 3,560,534 (1971) discloses transvinylation using a catalytic amount of a mercuric salt and perchloric acid. Mercury based transvinylation catalysts are also described in J. Org. Chem. 14, 1057 (1949); Org. Syn. 30, 106(1950); and Tetrahedron 24, 2205 and 3887 (1968), the latter reference stating that with a mercury salt, a strong acid such as sulfuric acid is necessary in the system.
Because of the toxic nature of mercury and mercury salts, considerable effort has been devoted to developing catalyst based upon other metals.
U.S. Pat. No. 3,188,319 (1965) discloses a transvinylation process which avoids the use of mercury by employing a catalyst of palladium acetate or a double chloride such as PdCl.sub.2 .multidot.LiCl. Because of the toxic character of mercury-based catalyst and the thermal instability of palladium-based catalyst, European Patent Application Publication No. 0,351,603 published January 1990, recommends the use of a ruthenium compound as the catalyst for transvinylation.
The instability of palladium catalysts is discussed by McKeon and Fitton, Tetrahedron 28, 233 (1972) who describe improved catalysts for vinylation of alcohols and carboxylic acids. Two catalysts prepared were diacetato (2,2'-bipyridyl) palladium(II) and diacetato (1,10-phenanthroline) palladium(II). Such catalysts are said to be advantageous because they do not form acetal by products which are observed using catalyst such as the palladium salts of strong acids, for example palladium chloride, which tends to be reduced to palladium metal during the reaction. Vinyl laurate was prepared from lauric acid and vinyl acetate using the palladium acetate complex with 2,2'-bipyridyl.
More recently Ketterline, et al., Applied Catalysis 66, 123 (1990) discussed vinylation of carboxylic acids by vinyl acetate using a catalyst of palladium acetate complexed with di-imine ligands to stabilize the catalyst and avoid its reduction to metallic palladium. Complexes were synthesized using 1,10-phenanthroline and 2,2'-bipyridyl as ligands. Vinylation of propionic acid was carried out with vinyl acetate. Addition of trifloroacetic acid did not change the rate of vinyl propionate production, thus showing no effect of Bronsted acidity.
Other approaches to solve the stability problem are described by U.S. Pat. No. 4,425,277 (1984) in which a binary catalyst system is used formed from a palladium compound supported on a solid carrier such as silica gel or active carbon with a cocatalyst consisting of a combination of an alkali metal compound and a copper(II) compound. Similarly, Allen et al., in Inorg. Chim. Acta., 28 (2), 231 (1978) disclose transvinylation reactions using as a catalyst palladium(II) salts supported on Amberlyst A21. Palladium compounds disclosed include sodium tetrachloro palladium.
A process variation is disclosed in British Patent 1,486,443 (1977) which describes a process for the production of a vinyl ester of an organic carboxylic acid with reactants chosen that the vinyl ester of the organic carboxylic acid has a lower boiling point than the vinyl ester used as an initial reactant. Consequently the product can be separated by distillation of the reaction products. The examples use a catalyst of a palladium chloride-lithium chloride salt or a mercury acetate with copper resinate.